London Underground Is Struck by Crude Bomb at Parsons Green

LONDON — Britain was hit by another terrorist attack Friday, when a crude device exploded on a crowded London Underground train, injuring commuters, sowing panic, disrupting service and drawing a heavy response from armed police officers and emergency workers.

The device exploded at 8:20 a.m. on a District Line train leaving the Parsons Green station in Southwest London.

“This was a detonation of an improvised explosive device,” Assistant Commissioner Mark Rowley of the Metropolitan Police, a top counterterrorism official, said at a news conference. He urged anyone who had seen what happened, or had taken photos or videos of the bombing, to come forward.

At least 22 people were hospitalized, several of whom had apparently been injured as panicked commuters fled. None had life-threatening injuries, and hospital officials described the victims as “walking wounded.”

“The train was packed, and I was down the other side of the carriage standing up, looking at my phone and then I heard a big boom and felt this heat on my face,” said Natalie Belford, 42, a hairdresser and beautician who was on the train. “I ran for my life, but there was no way out. The doors were full of people and the carriage was too packed to move down.”

A photo widely circulated on social media showed a white bucket inside a bag, with wires and flames coming out of it.

It was the fifth major terrorist attack in Britain this year.

Prime Minister Theresa May was monitoring the situation from 10 Downing Street and summoned a meeting of the government’s emergency committee, known as Cobra, for the afternoon. Boris Johnson, the foreign secretary, appealed for calm.

The city’s mayor, Sadiq Khan, issued a defiant statement on Facebook.

“Our city utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life,” Khan wrote. “As London has proven again and again, we will never be intimidated or defeated by terrorism.”

From the United States, President Donald Trump weighed in on Twitter, saying the bombing was the act of a “loser terrorist.” He said that “sick and demented people” had been “in the sights of Scotland Yard,” but he did not elaborate on what he meant.